CHAPTER II 



ASSIMILATION OF CARBON AND OF ENERGY BY PLANTS 



WITHOUT CHLOROPHYLL 



§i. General Discussion. — Most plants that are without chlorophyll and are, 

 in consequence, unable to assimilate the energy of sunlight, do not have the power 

 to transform non-combustible inorganic substances into organic compounds. 

 As will appear later, in order to form their various organic substances, green 

 plants require (besides carbon dioxide from the air and water from the soil) 

 nitrogen, potassium, calcium, magnesium, iron, sulphur and phosphorus, all of 

 which occur in the form of various salts in the soil. From the preceding dis- 

 cussion of chlorophyll (see Chapter I) it appears that no plant without chloro- 

 phyll can utilize the energy of sunlight to manufacture combustible organic 

 matter out of such substances. Most non-green plants must use, as sources 

 of both energy and material, organic compounds that have already been 

 formed; they are thus more nearly related to animals than to green plants, as 

 far as their nutrition is concerned. But organic compounds are not the only 

 substances that can be oxidized. This property belongs also to various inorganic 

 substances, such as ammonia, hydrogen sulphide and hydrogen, which thus 

 contain stored energy. As we have previously seen (page xxxii), the heat of 

 combustion of ammonia is greater than that of starch. The researches of recent 

 years have shown that such substances can serve as sources of nutrition for 

 certain plants without chlorophyll. On the basis of their mode of nutrition, 

 plants without chlorophyll may be divided into two groups: (i) plants that 

 derive their energy from organic compounds, and (2) plants that derive it from 

 inorganic substances. 



§2. Assimilation of Energy from Organic Compounds by Plants without 

 Chlorophyll. — Bacteria, yeasts, fungi and the non-green seed-plants, as well as 

 the non-green cells of green plants in general, obtain their nutrition from pre- 

 viously formed organic compounds, at least from previously formed carbohy- 

 drates. To study the nutritional requirements of these forms, culture media 

 containing various nutritive substances are employed. It was formerly thought 

 that the same nutrient medium should be suitable for all the simpler non-green 

 forms, but this is not so. In higher plants, specialization — i.e., adaptation to 

 surrounding conditions — is accompanied by peculiarities of external form as well 

 as of anatomical structure. On the other hand, the lower plants, such as bac- 

 teria and yeasts, are marked by their structural similarity and simplicity. It 

 was supposed, therefore, that such similarity of structure was accompanied by a 

 similarity in the characteristic life processes, and this, in turn, led to the supposi- 

 tion that the nutritive processes must be more or less uniform in these lower 

 forms. The most recent investigations have shown, however, that, in spite of 



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